Starter and Growth include automations. Go to Emails → Automations.
Create an automation and open the flow builder.
Start from a trigger (for example Added to supporter list).
Add steps: send email, wait, and (where supported) branch on events such as email opened.
Save and turn the automation on.
Tips
Link the campaign to the list in Campaign settings so new donors enroll automatically.
Email opened? steps need open tracking. That works with platform email delivery; it may not work if you send only through your own SMTP. The builder will warn you when a step is unavailable.
Test with a small list before a large send.
Enrollment counts appear on the automations list so you can see how many people are in the flow.